Make sure to include whole bash prompt in double quotes. If you put it in single quotes, the value inside parenthesis won't evaluate.
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user3173748Mar 11 '14 at 5:40

1

@user3173748 If you want something in the prompt to be evaluated on usage time, it has to be single quoted or at least escaped or it will be evaluated on definition. That aside, there isn't even anything in the question to be evaluated as it just shows, how the prompt should look like and not how it is defined.
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AdaephonMar 11 '14 at 7:26